The present invention relates to a writing instrument with an ink reservoir having an ink retaining portion for temporarily storing ink in accordance with change in the pressure inside the ink tank.
There are writing instruments having an ink retaining portion in its ink reservoir for temporarily storing ink in accordance with change in the pressure inside the ink tank.
A typical writing instrument, as disclosed in Japanese Utility Model Application Laid-Open Sho No.58-21474 and others, has a temporary ink retaining portion in front of an ink tank. This ink retaining portion is called xe2x80x98Jabara (bellows)xe2x80x99 and is formed of a multiple number of disk-like sheet elements arranged at intervals inside the barrel like a comb when sectionally viewed so that ink can be temporarily stored in the gaps between these sheet elements.
In the temporary ink retaining portion used in such a writing instrument, as sectionally shown in FIG. 1, the ink retaining portion is comprised of a multiple number of disk-like sheet elements xe2x80x98axe2x80x99 arranged in layers so that the spacing between layered sheet elements xe2x80x98axe2x80x99 will serve as ink retaining grooves. This ink retaining portion is fitted into a barrel cylinder xe2x80x98bxe2x80x99 and has a cutout portion xe2x80x98dxe2x80x99 formed in the rectangle direction with respect to the center line xe2x80x98cxe2x80x99 so as to create an air channel for establishing communication between the ink retaining portion and the outside air. In FIG. 1, a reference code xe2x80x98exe2x80x99 designates a common base of multiple sheet elements xe2x80x98axe2x80x99 as sectionally viewed and having a bore allowing an intermediary ink core xe2x80x98fxe2x80x99 to fit therein. Designated at xe2x80x98gxe2x80x99 is an ink conduit groove (slit) which establishes communication from an unillustrated tank to the ink retaining grooves so as to lead ink.
However, with the above-described conventional ink retaining portion, there have been cases where air replacement might be poor because the size of the cutout (air channel) is not large enough.
Further, when this ink retaining portion is formed by injection molding, the metal die element for molding is thin and sheet-like. Therefore, there has been a fear that the sheet-like metal die elements may give way or break as a result of the pressure arising when the resin is injected and it has been also difficult to produce an ink retaining portion having a large diameter.
The present invention has been devised in view of the above conventional problems and it is therefore an object of the present invention to provide a writing instrument in which a large-diametric ink retaining portion with air grooves small in width and still capable of securing a large enough air channel can be formed so that a sufficient amount of air will be able to be displaced between the ink retaining portion and the outside air.
The present invention has the following configuration in order to solve the above-mentioned problem.
The first aspect of the present invention resides in a writing instrument with an ink retaining portion for temporarily holding ink in accordance with change in the pressure inside the ink tank, comprising: a reservoir formed of sheet elements arranged at intervals in layers, wherein each sheet element is formed with a cutout which is formed to a right angle direction with respect to the center line of the sheet element and has a length equal to or greater than half the radius with one end extended to the periphery.
According to the configuration of the present invention, the following effect can be obtained.
According to the first configuration of the present invention, each sheet element is formed with the cutout which is formed to the right angle direction with respect to the center line of the sheet element and has a length equal to or greater than half the radius with one end extended to the periphery. Therefore, the forming die element of the cutout functions as the supporting bridge across the forming die elements for the grooves between sheet elements of the ink retaining portion, hence even if the cutout die element is large, no deficiency such as the mold yielding will occur when injection molding is performed.